1. Field of the Invention
The invention relates to trochoidal rotary expansible chamber devices having a planetating rotor and, more particularly, their construction and manufacture for approaching ideal expansion ratios.
2. The Prior Art
Trochoidal rotary expansible chamber devices, such as the Wankel or epitrochoidal rotary machines, generally comprise a housing defining a cavity in which is mounted a rotor rotatable in a planetating fashion. Trochoidal rotary devices may be divided into two groups referrd to as inner envelope and outer envelope types. In an inner envelope configuration, the profile of the housing cavity is the trochoidal curve and the peripheral profile of the rotor is the inner envelope of the trochoidal curve. In an outer envelope device, the rotor profile is the trochoidal curve and the housing cavity profile is the outer envelope of that curve. Variable spaces formed between facing peripheral surfaces of the rotor and housing cavity serve as working chambers for expansion engines, compressors, expanders, meters, etc. The working chambers are sealed with radially extending apex seals positioned along intersection lines between adjoining peripheral faces on the envelope curve surface. Typical apex seal arrangements for use in epitrochoidal inner envelope rotary machines are shown, for example, in Wankel U.S. Pat. No. 2,988,008 and Froede U.S. Pat. No. 3,139,072.
In currently produced rotary expansible chamber devices of the trochoidal type, apex seals are provided with curved profile sealing faces and mounted in the corresponding envelope apices such that the seal surfaces extend outward therefrom by a distance approximating their radii of curvature. The centers of curvature for the apex seal faces are located at the envelope apex points. Accordingly, the current manufacturing technique is to first generate an ideally desired trochoid curve profile and, then, recess the periphery by an amount equal to the outward extension or offset of the apex seals to be used. This offset amount can usually be characterized, in the case of apex seals having curved profile faces, as being one-half the width of the radial sealing elements or the radius of the face profile. The trochoid profiles are carved out by this seal offset amount in order to minimize seal reciprocation in the seal grooves, which tends to promote the formation of chatter marks and wear. This technique is described, for example, in the Wankel RC Engine (1st ed. 1969) by R. F. Ansdale at pages 81 and 133, and the Wankel U.S. Pat. No. 2,988,008. In some instances, it has been suggested that the trochoidal profile should be carved even more than the apex seal radial offset amount at selected portions of the profile periphery to prevent chattering, such as disclosed in the Froede U.S. Pat. No. 3,139,072.
The disadvantage of this current practice of recessing the trochoidal profile surface is that there is created an additional space to the working chambers which is never varied by movement of the rotor. Thus, the overall expansion ratios for current such rotary devices are significantly less than ideal. The present invention overcomes this deficiency by providing modified envelope surface which effectively eliminate seal offset clearance volumes and, thereby, approach ideal expansion ratios.